Magmatism controls bathymetry at global mid-ocean ridge-transform intersections

Ridge-transform intersections (RTIs) display distinct topographic morphologies, yet the origin remains debated. Standard thermal models treat the RTI as a juxtaposition of an old and cold plate against a young and warm spreading ridge such that this contact deepens the RTI with age offset, while another classic view attributed RTI bathymetry to spreading rate dependence of magma supply. These models explain the systematically deepening of RTI bathymetry with age offset and decreasing spreading rate, but fail to account for the highly variable RTI bathymetry with comparable age offset and spreading rate.

We analyzed multibeam bathymetric data of 101 RTIs at 65 OTFs at ultraslow- to fast-spreading ridges and conducted 3D numerical simulations of plate separation and dike injection at a ridge-transform-ridge system by using the geodynamic code LaMEM (Lithosphere and Mantle Evolution Model). We treat a dike injection to occur when differential stress that defined as the difference between magmatic overpressure and tectonic stress overcomes lithosphere pressure, which yields an effective M value that represents time-averaged fraction of plate separation accommodated by magmatic emplacement in a time scale of 10-100 yr. We show the variability in RTI depth can be related to brittle lithosphere thickness, where a thinner brittle lithosphere can generate the M value in a wider range and eventually leads to distinct topographic morphologies. This results in the systematically deepening of RTI bathymetry with age offset and its increasing variability with decreasing age offset. Furthermore, our result suggests that the systematical variations in RTI depth mainly reflects the age offset dependence of plate cooling, instead of spreading rate. More generally, it implies that the interactions between spreading ridge and the juxtaposed old plate determine time-averaged magma supply that reshapes seafloor morphology when oceanic transform faults pass mid-ocean ridges and evolve into fracture zones.